Abstract

A 3D visualization procedure based on micro computed tomography data revealed potential leak paths along the cement-rock interface. The rock-cement bonding was seen to clearly decrease with the presence of drilling fluid/filter cake. The core flooding experiments showed a correlation between the dimensions of interface micro-annuli and measured CO2 flow. However, unpredictable fluid migration was also observed – underlining the importance of understanding how drilling fluid and filter cake behave when subjected to downhole pressures. The results show the importance of updating well integrity procedures for CO2 storage wells in order to manage the risk of CCS projects. Our work shows the integrity of zonal isolation provided by annular and plug cement is difficult to achieve and that modeling with ideal assumptions on leak path shape and properties should be avoided.

1. INTRODUCTION

A properly designed and constructed well should have zonal isolation; meaning no detectable fluid migration across zones with different pressures. A simplified description of a petroleum well is a wellbore with steel casing(s) placed inside it. Cement is placed in the annulus between the casing and wellbore wall to mechanically support the casing, and to prevent migration of fluids from the reservoir. Over the years of petroleum production, the combination of hands-on experience and research has improved the understanding of cement as a material [1], and the procedures to prevent loss of zonal isolation [2]. Careful cement slurry preparation and use of spacers [3, 4], reciprocating/rotation of casing and casing centralization [5, 6, 7, 8], and control of the flow regime and fluid rheology [9] are some of the many important factors to increase the success rate.

This content is only available via PDF.
You can access this article if you purchase or spend a download.